IMHO, This is Ben Stiller's best film to date. He's good at the "Friends/RomCom" type films and really funny in so many others as well. With this one, it's him warts'n'all. This is Rhys Ifans best to date also. It's a good mix of drama and comedy.
I've just seen "The American" with George Clooney, which, I think, is George's sincere offering of something worthwhile. It's good and commendable. To compare the two films, Greenberg covers more ground and has characters that one can identify with.